Previously-known image display devices may include a plurality of image display sections each including a light source, a light modulation device, and a projection optical device. The light modulation device forms an optical image through modulation of luminous fluxes coming from the light source in accordance with image information, and the projection optical device extends and projects the formed optical image. The image display device of such a type displays an image being a result of overlay of at least a part of the projection areas of the optical images. Such an image display device is exemplified by a stack-type multi-projection system that includes a plurality of projectors, and displays, with an overlay, pixels of optical images formed through projection by the projectors. Another possible multi-projection system is of a type that displays, with a displacement, pixels of optical images in such a manner that a pixel of one optical image is located between pixels of another optical image. The light modulation device for use in the display section is exemplified by a liquid crystal panel, a device using a micromirror, and others.
The image display device equipped with a plurality of light modulation devices as such, however, may require adjustment of pixel positions in optical images formed by the light modulation devices through position adjustment of the optical images. To meet such requirements, a projection-type display device using a light shifting device, i.e., projection display device, has been available. As an example, refer to Japanese Patent Publication No. JP-A-6-123868.
With the projection-type display device of JP-A-6-123868, a light shifting device such as a flat transparent substrate is disposed on an optical path for luminous fluxes having been passed through the light modulation devices. Using the light shifting device, luminous fluxes of optical images formed by the light modulation devices are shifted in the direction orthogonal to the optical axis of the luminous fluxes, thereby adjusting the positions of the optical images projected on the screen.
One of the problems with such a projection-type display device of JP-A-6-123868 is that, when optical images formed by the light modulation devices do not all have the same characteristics, the optical images may not be easily adjusted appropriately in position. That is, when the projection-type display device is provided with two light modulation devices, and when position adjustment is so performed as to achieve position alignment between optical images formed by the two light modulation devices, one of the optical images is to be used as a reference for position alignment with the other optical image. Problematically, the projection-type display device of JP-A-6-123868 gives no consideration to the characteristics of the optical images formed by the light modulation devices. There is thus a possibility that the resulting synthesized image may not have a sufficient level of quality.